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Anatomy and Physiology of the Bladder

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The bladder is a sac-like organ in the pelvis that stores the urine produced by the kidneys. There are two tubular structures called ureters (one from each kidney) that drain the urine into the bladder. The urethra is the outflow tract of the bladder and connects the bladder to the exterior.

Anatomically, the bladder is the most anterior (closest to the front) organ in the pelvis, located just behind the pelvic bone. Organs closest to the bladder include the rectum (the last part of the colon), which is the most posterior (closest to the back) organ in the pelvis, the prostate gland and seminal vesicles (in males), and the uterus, ovaries and fallopian tubes (in females). In males, the prostate gland and seminal vesicles (organs that contribute secretions in semen) are situated below the bladder and in front of the rectum. In females, the uterus (the womb), ovaries and fallopian tubes are located posterior the bladder and anterior to the rectum.

The bladder itself is made up of four layers. These layers are important landmarks in determining how deeply the tumor has invaded and the ultimate stage of the cancer.
  1. Epithelium: The epithelium, which lines the bladder and is in contact with the urine, is referred as transitional epithelium or urothelium. Most bladder cancers originate from the cells of this transitional epithelium. The urethra, ureters and the pelvis of the kidney are also lined by this transitional epithelium, therefore, the same types of cancers seen in the bladder can also occur in these sites.

  2. Lamina propria: Under the epithelium is the lamina propria, a layer of connective tissue and blood vessels. Within the lamina propria, there is a thin and often discontinuous layer of smooth muscle called the muscularis mucosae. This superficial layer of smooth muscle is not to be confused with the true muscular layer of the bladder called the muscularis propria or detrusor muscle.

  3. Muscularis propria or detrusor muscle: This deep muscle layer consists of thick smooth muscle bundles that form the wall of the bladder. For purposes of staging bladder cancer, the muscularis propria has been divided into a superficial (inner) half and a deep (outer) half.

  4. Perivesical soft tissue: This outermost layer consists of fat, fibrous tissue and blood vessels. When the tumor reaches this layer, it is considered out of the bladder.

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